Methods of, this kind are used in motor vehicles for voice-enhancement duplex telephony or for supporting voice input-controlled electronic or electrical components. The fundamental difficulty that arises is that, depending on the particular operating state, background noise is present in a motor vehicle. It masks the voice commands. Intercom and two-way intercom or duplex telephony systems in motor vehicles are mainly used in large vehicles, minibuses, etc. However, they may also be used in normal passenger cars. When using voice-controlled input units for electrical components in motor vehicles, it is may be important for the background noise to be suppressed or for the voice command to be filtered out.
A voice-recognition device for a motor vehicle is described in European Published Patent Application No. 0 078 014, in which the status of engine operation and/or motor vehicle movement is signaled or fed in, via sensors, to the amplifier system of the voice-recognition device. Based on this, a noise-level control is used to attempt to filter out the voice command from the background noise.
A filtering operation is described in International Published Patent Application No. WO 97/34290, where periodic interfering noise signals are filtered out by determining their periods and by using a generator to interfere with them, so that the voice signal remains.
In German Published Patent Application No. 197 05 471, it is described to support a voice recognition with the aid of transversal filtering.
In German Published Patent Application No. 41 06 405, a method is described for subtracting noise from the voice signal, a multiplicity of microphones being used. A duplex telephony device having a plurality of microphones is described in German Published Patent Application No. 199 58 836.
In German Published Patent Application No. 39 25 589, it is described to use a multiple microphone system, in which, in motor vehicle applications, one of the microphones is placed in the engine compartment and one other microphone in the passenger compartment. A subtraction of both signals then follows. A disadvantage in this context is that only the engine noise or the actual running noise of the vehicle itself is subtracted from the total signal in the passenger compartment. Specific secondary noises are disregarded in this case. Also lacking is a feedback suppression. Everywhere that microphones and loudspeakers are placed in acoustically coupleable vicinity, the acoustic signal that is extracted, coupled out or decoupled at the loudspeaker is fed back, in turn, into the microphone. The result is a so-called feedback, and a subsequent overmodulation. Methods for avoiding such an overmodulation are described in European Published Patent Application No. 1 077 013, International Published Patent Application No. WO 02/069487 and International Published Patent Application No. WO 02/21817.
It is an object of the present invention to provide a method and a device that may improve the verbal communication among the occupants of a vehicle.